The use of inserts made of carbide are generally well known in the art. Various geometries have been proposed for such inserts which, for the most part, were to overcome problems associated with wear or deterioration. Various spherical or cylindrical geometries have been proposed such as U.S. Pat. Nos. 2,675,603, 3,537,491, 3,788,182 and 4,012,820. Other improved metal cutting geometries have been proposed in U.S. Pat. Nos. 3,576,061 and 3,576,200. Most importantly, the geometries proposed in U.S. Pat. Nos. 3,576,061 and 3,576,200 were shown to have increased the life of the blade as well as improved its metal cutting capability.
Generally, the geometry of U.S. Pat. No. 3,576,061 comprises a high tooth which has an outer central cutting edge at the top surface which intersects a negatively raked front face which is used to first remove a chip from the center of the kerf. Each high tooth is followed by a low tooth having a front face with a negative rake and two plane shearing faces that angle backwardly and flare laterally and outwardly from either side of the front face to remove two chips, one from each side of the kerf flanking the center chip. U.S. Pat. No. 3,576,200 provides a geometry for removing five chips from the kerf rather than three. The geometry taught therein comprises a high tooth having a central outer edge and two lateral cutting edges to remove three chips followed by a low tooth which includes two lateral cutting edges that are positioned between the outer and lateral cutting edges of the high tooth to provide two chips. The geometries taught in U.S. Pat. Nos. 3,576,061 and 3,576,200 provide circular saw blades which exhibit better metal cutting properties and longer life.
A suggested improvement over the triple-chip cutting teeth is set forth in U.S. Pat. No. 4,012,820 in which the working surface of the high and low teeth is arcuate rather than planar, but includes beveled top sides similar to U.S. Pat. No. 3,576,061. The principal advantage of the proposed design resides in the relative ease of grinding the arcuate working surface compared to three planar surfaces of the prior art.
Although it has been found that generally arcuate surfaces can be prepared with greater ease than a number of offset planar surfaces, planar working surfaces have been found to have better metal cutting characteristics and longer life than arcuate working surfaces. Accordingly, it is an object of the present invention to provide cutting teeth having planar working surfaces which have better metal cutting characteristics than the teeth disclosed in U.S. Pat. Nos. 3,576,061 and 3,576,200.